The present invention relates to the multiple access sharing of a single communication channel by multiple transmitters of digital information.
Spread ALOHA.TM.is a new connection-free multiple access technique which is described in detail in U.S. Pat. No. 5,537,397, SPREAD ALOHA CDMA DATA COMMUNICATIONS, by Norman Abramson, issued Jul. 16, 1996. Spread ALOHA Multiple Access (SAMA.TM.) may be viewed as a form of Code Division Multiple Access (CDMA) where each transmitter uses the identical spreading code and signals from various transmitters are separated at the hub receiver using a fundamentally different method than the code division employed in conventional CDMA networks. In a related patent application DUAL CODE MULTIPLE ACCESS FOR WIRELESS DATA NETWORKS, filed in the United States Patent Office on Jun. 19, 1996, Ser. No. 08/665,843, the basic idea of SAMA was extended to include the case where more than a single spreading code is used in the network.
The difference between Dual Code Multiple Access, as described in the above referenced patent application, and CDMA is that in a Dual Code Multiple Access network the different spreading codes are assigned to different classes of channel traffic or to two different branches of the transmitter (in phase and quadrature) in a QAM modulation system. Since the number of different codes required for that purpose can be many times less than the number of different codes required in a CDMA network Spread Aloha multiple access techniques are much easier to implement in networks with large numbers of potential transmitters.
In a Spread ALOHA multiple access network or in a Dual Code Spread ALOHA multiple access network the receiver at the hub station must separate transmissions from several transmitters which are transmitting at the same time. Since transmissions from different transmitters will ordinarily employ the same spreading codes, the hub receiver cannot separate those signals on the basis of the spreading codes as is ordinarily done in a CDMA network.